1. Field of Invention
The invention pertains to methods for modeling electronic device performance, and in particular to methods for modeling the performance of LDMOS devices.
2. Brief Description of Related Art
Accurate temperature scalable compact device models are the first steps towards designing extreme environment circuitry. Currently, designers utilize the standard models that are used to implement circuits in the 393 K to 218 K (+120° C. to −55° C.) range. Such models are not sufficient for applications that are to be deployed under deep cryogenic conditions (lunar, Martian etc.). The compact cryogenic model and the parameter extraction strategy is used to build high voltage biasing circuits for sensor interface electronics that are to be deployed in future lunar missions. These electronics are part of a remote health monitoring system-on-a-chip that monitors the conditions of surrounding key systems on a spacecraft [1]. This chip processes a wide variety of possible sensor inputs through an analog front end (Wheatstone bridge, variable gain amplifier, filtering, and data conversion). The electronics should be capable of operating down to 93 K (−180° C.) since they will not be shielded by “warm electronic boxes”, which is the current practice. This will greatly reduce weight, volume, and power consumption, while improving overall performance and system reliability.
It would be erroneous to extrapolate the temperature scaling in standard models to such low cryogenic temperatures simply because the behavior at 93 K deviates significantly from what was observed at 218 K. One approach to address this problem is to use a standard model as an iso-thermal model by turning off the temperature dependent parameters and extracting a parameter set to fit at one single temperature. This can be repeated at various temperatures within the range. This binning method has many disadvantages: (a) effects such as self-heating will not be accounted for, (b) may not be very accurate if many temperature points are not considered, (c) cannot be used to design circuits that require a continuous replication of the device performance over the temperature range, (d) would require greater time and effort for realizing the design, and (e) the possibility of human errors increase as designers need to repeatedly switch between the various iso-thermal models used in their circuits depending on the temperature. It would therefore be desirable to have one model (and thereby, one parameter set) that can accurately replicate the behavior of the device over the entire temperature range. These limitations of the prior art are overcome by the present invention as described below.